Well known cream liqueur products, such as Baileys Irish Cream, and the like, are basically emulsions formed from mixtures of aqueous alcoholic spirits and cream.
A recurring problem with such products is lack of emulsion stability, i.e., the ability of the two phases of the emulsion to resist change over a period of time and/or stress.
Emulsions may be defined as a mixture of liquids that are immiscible under ordinary conditions and which may separate into layers upon standing, heating, freezing, agitation or the addition of chemicals. Emulsions are basically two-phase systems. The phase which is present in the form of finely divided droplets is called the internal phase; the phase which forms the matrix in which these droplets are suspended is called the external phase. Cream liqueurs are emulsions which have butter oil (from dairy cream) as the internal phase, and a suspension of protein, buffering salts, flavorants and colorants in an alcohol/water mixture as the external phase.
One kind of emulsion instability is "creaming". This mechanism involves the rising of the dispersed (internal) phase to the surface of the emulsion. Factors influencing the rate and degree of "creaming" are the surface electrical charge of the globule, the relative sizes of the globules and the ionic balance of the external phase.
"Creaming" does not involve total breakdown of the emulsion and the layer of risen globules can be re-dispersed into the emulsion by simple agitation. However, repeated re-dispersion of the emulsion's components increases the tendency towards complete phase-separation.
Phase-separation, sometimes called syneresis, results from the coalescence of a few oversized globules, followed by agglomeration of the coalesced globules that are unable to return to the uniformly dispersed state. As these agglomerates become larger they form clumps. Phase-separated cream liqueurs lose their original flavor and texture characteristics and other important properties.
The effects of "creaming" in cream liqueur products, though undesirable, can usually be overcome by shaking or simple agitation. Phase separation, however, is a more serious problem. Phase-separation renders the cream liqueur product unsaleable and unuseable to consumers. Accordingly, emulsion stability is extremely important to the preparation of cream liqueurs having a commercially acceptable shelf-life.
The emulsion stability of cream liqueur products must be sufficient to avoid "creaming" and phase separation under normal handling, transportation, storage and use for such products. Therefore, such products must be stable to vibration, agitation, shaking, high shear, freeze-thaw cycling, elevated temperatures, dilution and, of course, be stable with the other constituents of the product itself such as salts, flavorings, colorants, alcohol, sugars, and the like.
Emulsion stability of cream liqueurs is a result of its composition and its mode of preparation.
It is known that the emulsion stability of cream liqueur products can be improved by adding stabilizing agents such as the sodium and/or potassium salts of citric acid as disclosed in the British Patent Application GB No. 2 084 185 A.
It is also known that, apart from their composition, the preparation of and processing of cream liqueur products, e.g., the mixing order, influences emulsion stability, hence, the shelf life. (Reference: Banks, W. et al. "Formulation of Cream-based Liqueurs: A Comparison of Sucrose and Sorbitol As The Carbohydrate Component." Journal of the Society of Dairy Technology, Vol. 35, No. 2, Apr. 1982, pp. 41-43).